Bryan R. Hollebone

SOLAR ENERGY STORAGE USING CHEMICAL POTENTIAL CHANGES ASSOCIATED WITH DRYING OF ZEOLITES

Abstract Compact solar storage systems depend upon identification of systems which can store energy as chemical potential. Simple, noncorrosive, systems that operate at reasonably low temperatures are rare. The use of the heat of adsorption of moisture on zeolite molecular sieves is discussed here. The advantages of zeolites are high heats of adsorption (as much as 80 kJ mol−1), large maximum adsorption capacity (0.2–0.3 kg H2O/kg adsorbent) and easy control of the store following from control of heat output by regulations of flows of moist air. The disadvantages are the relatively high upper temperature required to utilize maximal storage capacities (up to 250°C) and cost. There is reason to project falling cost. Zeolite storage is compared favourably with respect to capacity to water, stone, and heat of phase change systems. Compared to salt hydrates, acid solution, and salt solutions any capacity advantage is supplemented by low corrosion and opportunity for long term storage. Zeolites are compared favourably to alternative absorbent materials; alumina, charcoal, and silica gel. The warm dry air output from a zeolite storage bed can be utilized not only in space heating but also in the drying of agricultural timber and fish products.

THE RATES OF SOLAR ENERGY STORAGE AND RETRIEVAL IN A ZEOLITE-WATER SYSTEM

Abstract The salient features that determine the possible use of a water vapour-zeolite 13X system as a method of energy storage were investigated. Cycling studies over two months revealed no decrease in water capacity nor any structural deterioration. The rate at which water could be desorbed in a static situation was determined at various temperatures from 110 to 250°C. The adsorption isotherm and the heats of adsorption as a function of amount of adsorbed water were determined. The saturation capacity was 0.33 g H2O/g zeolite while the heat of adsorption declined from 90 to 50 kJ mol−1. The rate of heat development was found to be very high so that heat extraction from the store would not be a problem in any practical utilization of this system.

Assignment of absorption and magnetic circular dichroism spectra of solid, α phase metallophthalocyanines

Absorption and magnetic circular dichroism (m.c.d.) spectra of the α polymorphic form of a series of phthalocyanines CH2Pc, CoPe, NiPc and CuPc have been observed between 12 000 and 40 000 cm–1. Band shape analysis of both the absorption and m.c.d. data reveals Davydov splittings in both the Q and B (Soret) bands and suggests the existence of two π to π* transitions in the latter region. This lends support to previous assignments of the solution spectra of ZnPc. At higher energy no Davydov splittings are observed in the N band leading to a revised n→π* assignment.

Subduced selection rules for vibronic transitions ind3 octahedral complexes

Forbidden electronic transitions are often weakly allowed through vibronic coupling to normal modes of the molecule. In transition metal complexes, the first order strong coupling appears in many cases to select specifically one of the available asymmetric modes. In this work the Intermediate Ligand Field model has been extended to vibronic coupling. The basis functions and tensor operators are described as species subduced from the vibronic generative group SU(3) which results from the diagonal restriction of the direct product of the electronic generative group SU(2) with the three dimensional harmonic oscillator group SU(3). This model implies that transitions between strongly coupled bases are permitted only through an overall octupole operator. All lower multipoles are forbidden and in particular the dipole is eliminated by the requirement for a translationally invariant centre of mass. The model permits any combination of multipole operators for separate electronic and vibrational transitions which result in the overall octupole. This theory is applied to two cases ofd3 complex spectra. It provides an unambiguous assignment of the4A2g-4T2g transition in the absorption spectrum of solid [MnF6]4− and of the MCD spectrum of the4A2g-(2T1g,4T2g) region in [Cr(H2O)6]3+. In the latter complex, the observed exclusive coupling of the2T1g state tot1u (stretch) and the4T2g state tot1u (twist) is predicted by the model.

Effect of axially coordinated pi-acid ligands on photovoltaic properties of Zn-tetraphenylporphyrin

Following our earlier observations that the well known doping effect of oxygen and water on electrical properties of porphyrin and phthalocyanine films may be attributed to a pi-acid axial interaction throughout the film in the case of PdTPP, we have compared Zn-TPP films supported on transparent n-doped SnO2 electrodes which had been treated with several pi-acids in contact with an electrolyte to give photoelectrochemical cells. Photovoltages obtained in contact with a series of solution couples were used to obtain approximate photo flat band potentials. The doped films were examined by magnetic circular dichroism (MCD) spectroscopy so that the electronic effect of the dopant could be diagnosed. It was found that pi-acid dopants cause shifts to low energy in the band which indicates “hole stabilization” in the order pyridine < CO < triphenylarsine. The potentials of zero photopotential ‘EFB’, correlate approximately with spectral shifts. It is concluded that manipulation of axial ligand dopants is a promising method for design of metal porphyrin and perhaps phthalocyanine films with desired photovoltaic properties.

A central field interpretation of the absorption and M.C.D. spetroscopic parameters in arylcyanamocobaltate complexes

Abstract The electronic (absorption and MCD) spectra of a series of substituted tetrahedral tetrakis (phenylcyanamo)cobalt(II) complexes are interpreted to show an interrelationship between the ‘crystal field’ parameters, DQ, B and λ, which are usually taken to be independently variable. This relationship, satisfied adequately by the present data, is derived from a ligand field adaptation of crystal field formulae obtained via an identity transform of conventional LCAO radial wavefunctions which yields an approximate central field radial function dependent on an effective central charge, Z eff and effective quantum number, n eff . Since much chemistry has been rationalized by considering trends in DQ, B and λ as independent, the possibility of interrelationship is chemically non-trivial. Although the empirical scope of the approximations needed is not defined by the presently available data, they support the model sufficiently to warrant its careful evaluation.

The subduction of vibrational states of molecules from the momentum space of simple harmonic motion

A single-particle model of molecular vibrational states is proposed in which the normal modes are projected out of the body vibrations of an infinite simple harmonic sphere. This model assigns the spurious change of mass or centre of mass and leads to removal of mass monopoles and dipoles from the system. These conservation conditions impose strict boundary conditions on the potential and basis functions. On incorporation into the model they result in a set of loop equations in which the potential is proportional to the fundamental vibration. The simplest solutions to these equations strongly resemble the Poschl-Teller generalization of the Morse potential. The solutions have been extended to incorporate the repulsive states and generate the set of net attractive states appropriate to the anharmonic potential.The basis functions of this potential display both angular and radial node structures. The degeneracies between radial and angular mode patterns can be studied by transformation into an angular coordinate space. In this way coupling to other phenomena described in similar angular momentum space can be performed directly before subduction to real displacement space.

Analysis of the absorption and magnetic circular dichroism spectra of the hypertensive band in (h5C5H5)Ho(h8C8H8)

Abstract The solution MCD spectrum of ( h 5 C 5 H 5 )Ho(III)( h 8 C 8 H 8 ) is dominated by C terms but displays distinct A term under the hypersensitive 5 I 8 — 5 G 6 transition. Intermediate field analysis suggests this transition originates from the first electronic excited state and is enhanced by τ cyclopentadienyl ligand polarization.

Magnetic circular dichroism identification of four distinct species in the dehydration of cobalt(II) doped zeolite-A

M.c.d. spectra and thermogravimetry are used to reassign the species arising from dehydration of Na4Co4A (zeolite-A) as four distinguishable structures including a hydrated octahedral, a monohydroxo-tetrahedral, a hydroxo-dicobalt dimer, and a trigonal three-co-ordinate monomer species.

Intensity Enhancement Mechanisms in Ligand Field Spectroscopy and Relationships of Resulting Radial Fitting Parameters

In recent years the increasingly quantitative formulations of single-centre ligand field models which have arisen out of group theory and tensor analysis have provided a new formalism for the concise but detailed evaluation of ligand field parameters and transition selection rules. At first, vector coupling algebra was used only in atomic systems but was extended later in the weak ligand field form to lanthanide complex spectra. Still later it was applied in finite group form to transition metal complex properties and phenomena.